This invention concerns a machine for tying coils of metal wire which are produced in particular in metallurgical plants.
Tying devices are known in which clamps can be displaced parallel to the axis of the coil on the outside and inside thereof so as to form a loop around the coil with a tie wire, the two ends of this loop being then twisted.
Machines are also known which effect this tying by laying two ties parallel to each other, one on the outside of the coil and the other on the inside, and then twisting these ties at the two ends of the coil.
Other known machines have guide tubes, in which the tie is pushed in the direction towards a twisting head.
These machines have a number of drawbacks--the time for tying the tie is generally rather long and therefore poorly compatible with the rate of production of the coils to be tied.
The propelling of the tie wire in guide tubes results in a cold-working of this wire which may cause the breaking of the wire at the time of the tying. It is possible to use an annealed wire in order to avoid this drawback, but the cost of the tying would then be much too high.
Furthermore, guide tubes are subject to extensive wear and the systems for opening them in order to release the tie wire and tighten it around the coil are complicated and expensive. Moreover, the mechanical strength of the tyings obtained and the appearance of the twists are relatively unsatisfactory. The excessively protruding ends of the ties which are not bent over may, in fact result, in injuries and complicate the handling of the tied coils.
In the applicant's French Pat. No. 2,186,000 a device is described for the tying of coils of wires which comprises tying arms provided with clamps for grasping the end of the tie, said arms being mounted for rotation around a shaft supported by a carriage.
This carriage is movable in translation parallel to the axis of the coil and means are provided to pass one arm on the outside of the coil and the other arm on the inside of this coil.
This arrangement makes it possible to have the tie pass over the inner face and over the outer face of the wall of the coil.
These tying arms are satisfactory in most cases. However, these arms may be damaged when the coil is irregular (as is frequently the case) or poorly positioned with respect to these tying arms or when this coil contains wires which protrude into the inner cylindrical space of the coil.
In French Pat. No. 2,186,000 a machine has also been described which makes it possible to twist the ends of ties laid around the wall of the coil. The twisting means of this machine comprise a translatable and rotatable mandrel having a head which is adapted to receive the two ends of the tie, as well as a back-up plate arranged facing the head of the mandrel in order to hold the tie during the rotation of the mandrel.
This twisting device makes it possible to fasten the tie between the mandrel and the back-up plate, the latter remaining stationary during the twisting.
Due to the presence of this back-up plate this twisting device does not make it possible to obtain a very effective clamping of the ties against the wall of the coil.